The basic objectives of this research plan are: to define the quantitative alteration in interstitial and peritubular capillary dynamics that occur during the development and maintenance of hypertension in two kidney, one-clip renal hypertensive models, and to determine the changes in interstitial and peritubular capillary dynamics that occur during acute hypertensive states. This proposal is designed to allow evaluation of the role of peritubular capillary an interstitial fluid dynamics in the derangements of water and electrolyte reabsorption that occur during the development and maintenance of hypertension. The basic underlying hypothesis is the alterations in the microcirculation of the kidney may contribute to an inappropriate sodium and water excretory function in various forms of hypertension. Studies will be conducted on both dogs an rats made hypertensive by placement of a constricting clip or screw clamp on one renal artery. Emphasis will be placed on the evaluation of function in the contralateral kidney which is unprotected and subjected to the progressive development of hypertension. Measurements will be obtained at both hypertensive pressures and after reduction of arterial pressure to the normotensive range. In addition, the influence of differences in salt intake on interstitial and peritubular capillary dynamics of hypertensive animals will be determined. Studies will also be conducted in normal rats at normotensive pressures and at hypertensive pressures obtained by infusion of vasoconstrictors. Since the renin-angiotensin system has been documented to play an important role in the renal hemodynamic alterations observed in renal vascular hypertension, the possible role of angiotensin in the alterations in interstitial and peritubular capillary dynamics will be assessed with angiotensin blocking agents. A variety of whole kidney clearance and micropuncture techniques will be used to determine the quantitative characteristics of the peritubular capillary circulation and the renal interstitium as they are altered by hypertension.